1. Field of the Invention
The present invention relates to a method of manufacturing a copolymerized high polymer film capable of being used as an insulating film constituting semiconductor devices, a copolymerized high polymer film manufactured by such manufacturing method, and a semiconductor device using the copolymerized high polymer film. More specifically, the present invention relates to a method of obtaining vapor phase growth of copolymerized high polymer film through copolymerization on a surface, by using as raw materials more than two kinds of organic monomers having specific structures and supplying the same in vapor phase.
2. Description of the Related Art
Design rule of semiconductor integrated circuits continues to scale down, accordingly causing a gap between adjacent electrical wirings to come narrower. As a result, there arise more delays attributable to capacitance among electrical wirings, and hence there has been appearing an obvious deterioration of high speed performance in the operation of the integrated circuits due to such delays. Namely, in semiconductor integrated circuits, wiring signal delays are dependent on the wiring CR time constant (C: wiring capacitance; R: wiring resistance). In addition to an increase in wiring resistance due to a reduction in wiring width, the narrowed wiring gap causes an increase in the capacitance among the wirings.
When a wiring CR time constant in an electric circuit appreciably increases, it is concerned about a troublesome situation such that signal transmission speed on wiring may not sufficiently accord with the switching speed of transistors that constitute the circuit. Hitherto, aluminum alloy has been mainly used as a wiring material for semiconductor integrated circuits. In far miniaturized integrated circuits of great extent of integration, aiming at a faster operational speed and to avoid an increase in an electrical resistance of wirings due to the narrowed wiring width, it is necessary to lower electrical resistance of wiring material, and therefore employment of copper is currently preferred.
Meanwhile, in order to avoid an increase in capacitance at the gap among wirings, insulating film materials of lower degree of relative permittivity is now being adopted, rather than silica (SiO2) based insulating film that has been widely used till now. As an insulating film material of low relative permittivity, use of fluorine added silica (SiOF) or organic high polymer film (organic insulating film) as the above-mentioned insulating film materials disposed between wirings of the semiconductor devices, comes into practice.
For example, fluorine added silica is already used in certain products on market For the purpose of enhancing the low permittivity of fluorine added silica materials, if fluorine concentration is increased, it causes a corrosion of wiring metal by hydrogen fluoride generated in reaction of fluorine with moisture or hydrogen. Otherwise, as a result of dissociation of fluorine, such a problem as increased relative permittivity will arise anew.
In addition, due to further progress of technology in semiconductor integrated circuits, demand for lower permittivity of wiring insulating film material is no longer satisfied sufficiently with the relative permittivity of around 3.3, now being available by fluorine added silica (SiOF). That is to say, attention is now focused on usage of an insulating material having such a very low relative permittivity as below 3.
On the other hand, an organic high polymer film, compared with the above mentioned silica-based materials, is lower in relative permittivity of the material itself and hence is advantageous when used as an insulating material of low permittivity. Further, with appropriate selection of the structure or type of organic chemical compound, or polymerization condition thereof, it will be possible to provide desired functions. Accordingly, organic high polymer films have been developed, which may be utilized as an interlayer insulating material of low permittivity, which is to insulate the gaps among multilayer wirings in semiconductor integrated circuits.
As a film-forming method adapted for functional organic high polymer films, there is Spin-Coating Method, in which raw material organic monomers are subjected to spin-coating and subsequently, are copolymerized within the coated layer resulting in forming of a high polymer film. The organic monomers per se mean raw material chemical compounds, which are to constitute an aimed organic high polymer (organic polymer) by polymerization reaction of such organic monomers as constituent units. The Spin-Coating Method is a method extensively used for film-forming of an organic high polymer film.
In this particular method, for the purpose of performing the spin-coating, organic monomers are dissolved in solvent, which is to be removed by evaporation in the film-forming process after the coated layer has been formed, and an inter-monomer polymerization reaction of the remaining organic monomers by heating are preceded. Finally, formed by polymerization reaction is a film of two-dimensional or tree-dimensional network structure or a high polymer film, which involves the organic monomers as constituent units. Composition and structure of the organic insulation film manufactured by the described Spin-Coating Method are determined by structures of organic monomers per se dissolved in the organic solvent used for the spin-coating as well as content ratio of plural kinds of the organic monomers.
For example, in “REAL-TIME FT-IR STUDIES OF THE REACTION KINETICS FOR THE POLYMERIZATION OF DIVINYL SILOXANE BIS BENZOCYCLO BUTENE MONOMERS” (Material Research Symposium Proceeding Vol. 227 p. 103, 1991) T. M. Stokich, Jr., W. M. Lee, R. A. Peters. (hereafter referred to as Non-Patent Document 1.), there is a description such that divinylsiloxane-bis-benzocyclobutene monomer is dissolved in solvent of mesitylene, and the resultant solution is applied to do the spin-coating, then is baked at 300° C.-350° C. for permitting a thermal ring-opening reaction of four-membered carbon ring of benzocyclobutene skeleton in the raw material monomer molecules to takes place, resulting in film-forming of an organic high polymer consisting of a three-dimensional molecular chain of divinylsiloxane bis-benzocyclobutene monomer being skeleton.
In the Spin-Coating Method, organic monomers are dissolved in an organic solvent and resultant solution is applied to spin-coating and accordingly, approximately 90% of such solution used in the spin-coating process is dispersed out of substrate. Therefore, with regard to organic monomers as starting materials, it is a method of low efficiency. Accordingly, cost percentage of organic monomers of starting materials against total production cost will become relatively high. Solvent is usually of volatile organic compounds, and is used in large quantities. Hence, a local exhausting facility is required to be installed at the site. In spin-coating or solvent removal process, it will be necessary to provide additional processes or facilities for control of environment, or for control or elimination of airborne fine dust particles or dispersed, dried and solidified fine particles of monomers, which will reflect upon production cost. In case that control of environment or elimination of fine particles is insufficient, it will be liable to deteriorate the characteristics or reliabilities of organic high polymer film thus formed.
Further, Japanese Unexamined Patent Publication (Kokai) No. 11(1999)-017006 (hereafter referred to as Patent Document 1.) describes a vapor-phase growth method of organic monomers as a film-forming method of functional organic high polymer film utilizing a vapor-phase growth method.
The described vapor-phase growth method of organic high polymer film vaporizes raw material organic monomers to feed monomer molecules in vapor phase and performs an inter-molecule thermal polymerization of the monomers on a substrate to obtain an organic high polymer film.
Such a film-forming method of organic high polymer film by, so-called, the organic monomer vaporization method, as described in the Patent Document 1, is different from the Spin-Coating Method, in that the organic monomer vaporization method does not utilize an organic solvent and also performs film-forming in a decompressed reaction chamber where oxygen does not exist in the atmosphere. Therefore, the organic monomer vaporization method has excelled in the sense that it is essentially free from a cause to deteriorate the quality of film, such as possible reaction with oxygen, or possible generation of foams or voids within the film attributable to a vaporization of organic solvent as may be observed in case of the Spin-Coating Method. Also, when substrate temperature is raised in an attempt to increase the degree of polymerization, or to increase the velocity of polymerizing reaction, organic monomer molecules once adsorbed, to the contrary, increases the velocity of desorption, hence, reducing the effective velocity of adsorption onto the substrate. Thus, technical difficulty still remains with the unresolved enhancement of growth rate yet to achieve.
Further, Japanese Unexamined Patent Publication (Kokai) No. 2003-012776 (hereafter to be referred to as Patent Document 2.) describes a film-forming method of copolymerized high polymer, which makes effective use of the principle of plasma polymerization. Namely, using a plurality of organic chemical compounds, and controlling the respective feeding ratios in a plurality of raw materials, a wide variety of copolymerized high polymer films can be formed with continuously differentiated microstructure of polymer in the direction of thickness to be formed.
This method excellently enables not only to achieve high adhesion properties with other semiconductor materials but also to further reduce relative permittivity of organic high polymers, as a whole, when organic polymer film is utilized as insulating film for low permittivity interlayer.
Furthermore, Japanese Unexamined Patent Publication (Kokal) No. 2000-012532 (hereafter referred to as Patent Document 3.) describes a plasma polymerization method as a film-forming method of functional organic high polymer film, which has further extended the development of vapor phase film-forming method of organic monomers as described in the Patent Document 1.
In the plasma polymerization method described in the Patent Document 3, organic monomer transported in vapor phase is excited to increase reactivity, when it passes through plasma, and reaches the substrate in an excited state to begin polymerization reaction over the substrate. Therefore, the film formed over the substrate is a film with structure of organic monomers in skeleton as the starting raw material, and the thickness of the formed film can be controlled at a high accuracy with a high reproducibility simply by controlling an amount of organic monomer to be supplied. However, the plasma polymerization method or the plasma copolymerization method described in the Patent Document 2 or 3, respectively, is useful as forming method of organic polymer film that can be utilized as a low permittivity interlayer insulating film, while there are not so many known organic chemical compounds that can be utilized as its raw materials. There are no more than several kinds of organic chemical compounds known as described in the Patent Document 2.
The properties required for a low relative permittivity interlayer insulating film are not only low relative permittivity but also a high thermal resistance, a high mechanical strength, a practical film forming speed, a high adhesion property with other semiconductor device materials and so forth. The demand for the properties of the low relative permittivity materials is as high as those for conventional materials of relatively high permittivity. To comply with such demand in film-forming of a low permittivity organic polymer film as described in the Patent Document 2 or Patent Document 3, it is necessary to provide a highly sophisticated technique in controlling the film quality as well as film structure. Nevertheless, with conventionally known organic monomers, there was an inevitable limitation in acquiring specifically low relative permittivity, while keeping a high film-forming speed and a high mechanical strength as stated in the above.